The present invention relates generally to an apparatus and method for cooling a venturi used in the combustion chamber of dry-low NOx gas turbine engine combustors.
In a typical dual-stage, dual-mode gas turbine engine a secondary combustor includes a venturi configuration to stabilize the combustion flame. Fuel (natural gas or liquid) and air are premixed in the combustor premix chamber upstream of the venturi and the air/fuel mixture is fired or combusted downstream of the venturi throat. The venturi configuration accelerates the air/fuel flow through the throat and ideally keeps the flame from flashing back into the premix region. The flame-holding region is necessary for continuous and stable fuel burning. The combustion chamber wall and the venturi walls before and after the throat region are heated by a combustion flame and therefore must be cooled. In the past, the venturi has been impingement-cooled by combustor discharge air at the forward end, and turbulator-cooled in an axially aft portion of the venturi, downstream of the throat region.
In recent tests of certain turbine engines, however, it has been observed that vortex shedding at the venturi dump (where the venturi cooling air joins with the combustion gases exiting the combustor) has a tendency to interact with the flame and produces dynamics, or screech tones. These vortices are shed from the venturi turbulators and preliminary indications suggest that eliminating the turbulators at the aft portion of the venturi assembly will lead to a reduction or elimination of the vortex shedding, and thus also a reduction in screech tone frequencies.